To produce a hollow glass article, a gob of molten glass is deposited inside a mold, and at least a preliminary outwardly open cavity is formed in the glass gob, normally by means of a punch assembly comprising a punch member, which is inserted inside the mold and the molten glass gob, and a normally pneumatic or hydraulic actuating device for moving the punch member to and from the mold in a vertical direction.
Though widely used, pneumatic or hydraulic actuating devices have various drawbacks, all related to the use of pressurized operating fluid. At present, such drawbacks are at least partly solved by the solution described in European Patent Application n. EP 0 789 004, which relates to an electric punch assembly, in which the punch member is driven by a rotary electric motor aligned and coaxial with said vertical direction, and connected to the punch member by a screw-nut screw transmission.
While solving the operating fluid problems of former devices, the above electric assembly is of only limited success by only applying to certain types of molding machines, and, in particular, by calling for major alterations to existing machines which are not always possible.
The reason for this substantially lies in the considerable axial size, i.e. measured in the traveling direction of the punch member, of the above electric assembly, which therefore cannot be inserted in the space available on existing molding machines, which, as is known, is defined at the top by the mold and at the bottom by the mold opening/closing assembly.
The electric actuating assembly of the above patent application is also relatively complex to produce and difficult to assemble, thus complicating not only routine maintenance but even straightforward replacement of both the electric motor and the screw-nut screw transmission which, with wear, inevitably introduces slack in the gearing between the electric motor and punch member. In some cases, the motor and the screw-nut screw transmission reach the end of their working lives in times which may differ widely—mainly on account of the motor being located adjacent to the mold, inside a closed chamber, and therefore in a high-temperature environment—so that they must be replaceable independently and quickly without having to dismantle the whole assembly, which conditions are not met by the known electric-motor punch assembly.
Moreover, known electric actuating assemblies are difficult to apply in the case of multiple-mold sections, i.e. when each molding section comprises two or more adjacent molds for producing two or more articles simultaneously. In such cases, a number of adjacent punch assemblies—one for each mold—must be set up and so positioned that the distance between the axes of each two adjacent molds is exactly the same as that between the traveling directions of the relative punches. Given the considerable transverse dimensions of known punch assemblies and the need to align the motor, the motion conversion assembly and the punch member, such an arrangement is not always possible, so that known punch assemblies are rejected even at the design stage.